Two issues with opening binary files. 1) when I (accidentally?) open a binary executable file it often kills my w98 X server. I get X errors like this just before the demise: xemacs: X Error of failed request: BadDrawable (invalid Pixmap or Window paramete r) Major opcode of failed request: 64 (X_PolyPoint) Resource id in failed request: 0x4c010005 Serial number of failed request: 36624 Current serial number in output stream: 38278 xemacs: X Error of failed request: BadLength (poly request too large or internal Xlib length error) Major opcode of failed request: 92 (X_LookupColor) Serial number of failed request: 36625 Current serial number in output stream: 38278 So, opening binary files is bad, so I decided to write an advice type thing to open the executable in hexl mode. ;; Open files that begin with 'ELF' in some other mode. (defvar executable-pattern (concat "^" (regexp-opt (mapcar 'regexp-quote '("\177ELF")) t))) (defadvice set-auto-mode (around look-for-executables first activate) (if (save-excursion (goto-char (point-min)) (looking-at executable-pattern)) (hexl-mode) ad-do-it)) This seemed to work fine until tar mode came along: (defun tar-set-auto-mode () (interactive) (if (and buffer-file-name (string-match tar-regexp buffer-file-name)) (tar-mode) (tar-real-set-auto-mode))) (if (not (fboundp 'tar-real-normal-mode)) (fset 'tar-real-normal-mode (symbol-function 'normal-mode))) (fset 'normal-mode 'tar-normal-mode) (if (not (fboundp 'tar-real-set-auto-mode)) (fset 'tar-real-set-auto-mode (symbol-function 'set-auto-mode))) (fset 'set-auto-mode 'tar-set-auto-mode) Tar mode redefines set-auto-mode with different arguments and was completely antisocial with my advice. So, the questions are 1) Is there/Shouldn't there be a hook for catching binary files and displaying them in a default 'binary' mode, like hexl. 2) shouldn't set-auto-mode have some sort of pre hook that lets arbitrary hooks be tried until one of them returns true eg 'run-hook-with-args-until-success'. Tar mode would be a hook that intercepts files that end with .tar -jeff